The Molotov–Ribbentrop Pact, named after the Soviet foreign minister Vyacheslav Molotov and the German foreign minister Joachim von Ribbentrop, officially the Treaty of Non-aggression between Germany and the Union of Soviet Socialist Republics, was a non-aggression pact signed between Nazi Germany and the Soviet Union in Moscow on 23 August 1939. It is also known as the Ribbentrop–Molotov Pact or Nazi–Soviet Pact.The pact remained in force until the German government broke it by invading the Soviet Union on 22 June 1941.The pact's publicly stated intentions were a guarantee of non-belligerence by each party towards the other and a commitment that neither party would ally itself to or aid an enemy of the other party. In addition to stipulations of non-aggression, the treaty included a secret protocol that divided territories of Romania, Poland, Lithuania, Latvia, Estonia, and Finland into German and Soviet ""spheres of influence"", anticipating potential ""territorial and political rearrangements"" of these countries. Thereafter, Germany invaded Poland on 1 September 1939. After the Soviet–Japanese ceasefire agreement took effect on 16 September, Stalin ordered his own invasion of Poland on 17 September. Part of southeastern (Karelia) and Salla region in Finland were annexed by the Soviet Union after the Winter War. This was followed by Soviet annexations of Estonia, Latvia, Lithuania, and parts of Romania (Bessarabia, Northern Bukovina, and the Hertza region). Concern about ethnic Ukrainians and Belarusians had been proffered as the reason for the Soviet invasion of Poland.Of the territories of Poland annexed by the Soviet Union between 1939 and 1940, the region around Białystok and a minor part of Galicia east of the San river around Przemyśl were returned to the Polish state at the end of World War II. Of all other territories annexed by the USSR in 1939–40, the ones detached from Finland (Karelia, Petsamo), Estonia (Ingrian area and Petseri County) and Latvia (Abrene) remained part of the Russian Federation, the successor state of the Soviet Union, after 1991. Northern Bukovina, Southern Bessarabia and Hertza remain part of Ukraine.The existence of the secret protocol was denied by Soviet leadership until 1989, when it was acknowledged and denounced. Some time afterwards the Russian historiography has been inclined to describe the pact as a necessary measure. This includes books by Alexander Dyukov, and one edited by N.A. Narochnitskaya that carries an approving foreword by Russian foreign Minister Sergei Lavrov. Vladimir Putin has defended the pact as well.